The principal elements of the more important cement materials are
lime, silica and alumina.
The raw materials which supply these elements are, more especially:
Limestones, which contain the lime ; marls, which contain lime and at
the same time, silica and alumina ; clays, pozzolaiic and other similar
materials, and blast-furnace dags, which contain the silica, and alumina.
The. cement materials composed essentially of lime are the/a/ and lean
or poor limes. Materials containing, besides lime, marked proportions of
silica and alumina (clay), that is, the hydraulic limes and the cements, have
hydraulic properties, setting even under water when properly mixed. Of
these the hydraulic, limes are poorer in clay than the cements and set more
(iypsnm, obtained by burning' the hydrated calcium sulphate which
occurs abundantly in nature, also occupies a, place among the cement
LIMESTONES AND MARLS
Limestones are rocks composed mainly of ealcimn carbonate. Their
most common impurities an- silica, and alumina- the constituents of clay
•-•-and ferric oxide, and alumina, ; they may also contain small quantities
of alkalies, sulphates, sulphides, carbonaceous and bituminous substances
and other impurities. Limestones containing marked quantities of clay
are termed argillaceous ; the name marl is used in cases where the clay is
in such proportion that it cannot be regarded as an impurity, (lie material
being a natural and intimate mixture of limestone and clay.
Analysis of these materials aims principally at establishing (he amounts
of calcium carbonate and argillaceous material present, and in the second
place at determining the quantities of the various accessory components.
Such analysis may be partial or complete. The former is far more
rapid and is preferred in practice, when determinations are required only
of the principal constituents and great accuracy is unnecessary. method ; the. total nitrogen, by the IJlsch (or